float collar

A component installed near the bottom of the casing string on which cement plugs land during the primary cementing operation. It typically consists of a short length of casing fitted with a check valve. This device may be a flapper-valve type, a spring-loaded ball valve or other type.
The check-valve assembly fixed within the float collar prevents flowback of the cement slurry when pumping is stopped. Without a float collar, the cement slurry placed in the annulus could U-tube, or reverse flow back into the casing. The greater density of cement slurries than the displacementmud inside the casing causes the U-tube effect.